Does your employer not (optionally) manage your 401k? Mine has been doing better than my other accounts on index funds.
I have to believe that if a company is "managing" 401k investments, it's just an abstraction on top of some agreed-to investment strategy at the brokerage.
Rollovers typically only happen after employment has ended.
https://www.investopedia.com/terms/i/inservicewithdrawal.asp